Shipping containers used in -inland America are typically 53 feet in length so that a semi-trailer for transporting the container should be greater than 53 feet. Semi-trailers are often made in China and then transported to United States by ship. There are two methods for shipping. The first method is to use bulk cargo ships and the second method is to use container vessels. By using bulk cargo ships, the semi-trailer can be transported integrally. However, using the first method occupies large space and freight is high. Additionally, the shipping frequency of the bulk cargo ship is too low to meet delivery requirements. With the second method, although the shipping frequency of the container vessels is high and the freight is low, there are limitations on the goods with extreme length because the length of the standard container is 20 feet or 40 feet. Therefore, for shipping the semi-trailer of 53′ by using the standard container vessels, the semi-trailer is segmented into two or more parts. The semi-trailer is transported in parts by the containers and assembled after arriving at United States to form an integrated 53′ container semi-trailer.
FIG. 1A illustrates a connected two-segment main beam of a containers semi-trailer of 53′. Because the main beam of container semi-trailer is too long to transport, it is segmented into two parts, i.e. a front beam 10 and a rear beam 20, or more parts. After reaching the destination, the front beam 10 and the rear beam 20 are assembled by a joint 30 to form the complete main beam of a 53′ container semi-trailer.
FIG. 1B illustrates the structure of a disconnected conventional joint for connecting the main beam of container semi-trailers. The main beam of container semi-trailer is in the form of I-shaped steel. The conventional joint 30 comprises a first connecting plate 31 welded on the cross section of an connecting end 11 of the front beam 10, and a second connecting plate 32 welded on the cross section of an connecting end 21 of the rear beam 20. Two ribs 331, and 332 spaced apart in an upright direction, are provided at an inner side of the connecting plates 31 and 32 to prevent the connecting plates 31 and 32 from deforming when connected by the bolts.
FIG. 1C illustrates a connected conventional joint. When connecting, the joint of the front beam 10 and the rear beam 20 are aligned with each other, and the connecting plates 31 and 32 are closed up with each other. Afterwards, as shown in FIGS. 1D and 1E, six bolts 33 are inserted into six bolt holes 311 and 321 and tightened by a fastening tool to form a complete main beam. It can be seen from the drawings that in this structure, the bolts bear all the forces transferred to the connecting plate when the container semi-trailer is running.
In the prior art, the main beam is segmented into several parts to meet the requirements of transporting, and after reaching the destination joints are used to reassemble the main beam. The conventional joint mentioned above comprises a connecting plate welded on the cross section of an end of the main beam, and three pairs of bolts are used to fix said joints to form a complete main beam structure. Although this is a simple and practical connecting method, during running of the container semi-trailer, the main beam is often in situations of being stretched, bent, twisted, or sheared etc. alternately. The top and the bottom pair of bolts have the biggest stress, which may cause one or two of the bolts bear very large force which may even exceeding the yield limit of the bolt. As a result, the bolts are deformed or destroyed thus cause the connection failure.
Generally, it is urgent to develop a more reliable joint and main beam of container semi-trailer for segmented container semi-trailer with an extreme length.